The conventional fixed wrench is generally composed of a handle and an open end which is located at one end of the handle and provided with two jaws for holding and turning a fastening piece of a specified specification. Such a conventional fixed wrench can not be therefore used in turning the fastening pieces of other specifications.
A prior art fixed wrench is capable of turning two fastening pieces which are slightly different in size due to the fact that the sizes of these two fastening pieces are measured respectively by the English system and the metric system. Such a fixed wrench is limited in its use.
Another prior art fixed wrench has a box end which is provided with a corrugated engagement slot for turning the fastening pieces of various sizes. However, the fastening pieces can not be easily turned by a wrenching movement of the fixed wrench due to the small contact area of the engagement slot. As a result, the fastening pieces are often vulnerable to damage caused by an ineffective wrenching movement of the fixed wrench.